The invention relates to a surface treatment method, in particular for the surfaces of hard bodies and condensed media. It,likewise relates to a device for implementing the method.
The method and device according to the invention may be used in particular in the electrical engineering sector, in electronics, the chemical industry, the foodstuffs industry, machine tools, medicine, pharmaceuticals, and in particular for operations involving cleaning, sterilisation, pickling, the deposition of films, surface alloys, etc.
A treatment method is known for solid surfaces by means of plasma under vacuum, in the course of which a stream of activated particles is formed at low pressure. This method is described in the document xe2x80x9cThe iono-plasmic treatment of materialsxe2x80x9d, Ivanovskii G. F. and Petrov V. I., Moscow 1986. This particle stream acts on the surface of the solid body and the volatile products resulting from the interaction of the plasma are evacuated from the reaction zone. The composition of the plasma is selected on the basis of the intention behind the treatment. In order to increase the effectiveness of the operation by plasma under vacuum, the kinetic energy of the particles is increased up to 100 eV and above, which causes the appearance of flaws due to the destructive bombardments of the structure of the surface being treated. This treatment, which requires the maintaining of the vacuum, is used for preference in situations in which the surfaces to be treated are of restricted dimensions, in particular in the electronics industry.
A dynamic plasma treatment method (Dynamic Plasma Operation or DPO) is likewise known. This method is described in the documents xe2x80x9cDynamical Plasma Operating (DPO) of solid surfaces plasma jetsxe2x80x9d, Koulik P. P., ed. Solonenko O. P., Fedorchenko A. V., Frunze VSP 1990, pp. 639-653, and xe2x80x9cDynamical Plasma Operating (DPO) of solid surfaces plasma jetsxe2x80x9d, Koulik P. P. et al., ed. Nouka, 1987, pp. 4-13, 58-96. This consists of creating a hydrodynamic stream of activated particles, directing them towards the surface to be treated, causing them to react with this surface, and evacuating the volatile products accompanying the reaction, making use of the hydro-dynamic stream pressure; i.e. at high pressure. The surface treated by this method is subject to the action. of high-enthalpy stream, which contain active particles (pickling, cleaning, depositing of films, etc.).
The approximate values of the parameters of the plasma stream are as follows:
Temperature: 8xc2x7103-15xc2x7103 K
Speed: 100-200 m/s
Density of heat flow on the surface, oriented perpendicular to the stream:
1024-1025 particles/m2xc2x7s
For these plasma stream parameter values the interaction of the plasma with the surface can only be momentary, and does not exceed 10 ms. The treated object passes through the plasma stream at a controlled speed (approx. 1 m/s) in such a way that, for transient heat transfer, the maximum surface temperature does not exceed a given limit. According to the technological operation concerned, this temperature level may be several tens of degrees, or even several hundreds of degrees.
Since the duration of the DPO method is less than the characteristic diffusion time in the solid body, the DPO treatment does not induce flaws in the structure of the solid body treated.
Since the temperature of the electrons on the surface of the body or medium being treated does not exceed 0.08 eV, and that of the ions, atoms, and other heavy components does not exceed 0.03 eV, it follows that radiative flaws of the structure of the surface layer treated will be excluded.
The principal physical energy of the DPO method is expressed by the two inequalities:
lr less than  less than d less than  less than linxe2x80x83xe2x80x83(1)
where lr is the mean length of the free path of the plasma particles, d is the thickness of the limit layer at the critical point, and lin is the mean diffusion length of the activated particles of the plasma. The left inequality ensures the continuity of the plasma medium, and that on the right the maintaining of imbalance necessary for an effective plasmo-chemical action on the surface.
The DPO method is easy to use, in particular at atmospheric pressure. Passage at atmospheric pressure allows for the productivity of the treatment to be enhanced by 10 to 100 times by comparison with the vacuum plasma process. The quality of the treatment is greater and the technology simplified.
Nevertheless, the DPO method can only be used under the following conditions:
The treatment is applied by a high-enthalpy plasma jet;
Stationary cooling of the objects treated is excluded, and it is necessary to work under non-stationary heat exchange conditions; i.e. to submit the treated surface to a momentary plasma action.
These conditions perceptibly restrict the possibilities of this technology, and render the treatment of many materials difficult.
The objective of the invention is to broaden the choice of materials which can be treated, to make new surface treatments possible thanks to the separate monitoring of the activated and stream-modifying functions, and also to broaden the ranges of the physical parameters of the streams used for the treatment.
To this end, the invention relates to a surface treatment method, in particular of the surfaces of hard bodies and condensed media, in the course of which a stream or streams of activated particles is or are created, and directed on to the surface to be treated, and the particle streams are caused to interact with the surface, and in which the stream(s) of activated particles is (are) composed of activated particles, forming chemically active sites on the surface, and modifying particles occupying these sites, the energy of the activated particles being greater than the energy at break of the inhibited surface bonds of the treated surface, and lower than the radiative flaw formation energy on the surface, the intensity, at the level of the surface treated, of the stream of activated particles and the stream of the modifying particles being greater than the value N/t, where N is the surface density of the inhibited bonds to be broken, and t is the presence time of any point on the treated surface, under the stream.
The invention likewise concerns a device for surface treatment for the implementation of the method, comprising a device for introducing the active product from an active particle stream generator, including an energy source, a reactor creating the stream of activated particles, a medium for transporting the activated particles generated to the treated surface, and a medium for evacuating the residue products of the treatment, and in which the active particle generator comprises:
a) Two reactors, the first creating a stream of activated particles, which, when coming in contact with the treated surface, form chemically active sites, the second creating a stream of modifying particles which have just occupied the sites;
b) Two transport devices for the activated and modifying particles respectively by means of flows carrying the activated and modifying particles onto the treated surface, the duration of transport of the activated and modifying particles from the reactor to the surface to be treated being less than their respective life time durations;
c) A device for the relative displacement of the surface treated in relation to the streams of activated and modifying particles, ensuring that the time lapse between the activation and modification actions of one common area on the treated surface is less than the life time of the activated sites created by the activated particles, and that the areas of the surface to be treated, being first in contact with the stream of activated particles and then only with the stream of modifying particles;
d) Two evacuation devices, one for the activated particles deactivated after their action on the treated surface, the other for the residual particles appearing after the action of modification of the surface, the two systems being conceived in such a way that the evacuation of the one group will not cause any obstacle to the action or evacuation of the others.
According to one embodiment, the activated particles coincide with the modifying particles, which allows the generator device to be reduced to an introduction device, a reactor, a transport device, a device for displacement relative to the surface, and an evacuation device.
According to a variant embodiment, the reactor, the transport and evacuation devices may be common for the activated particles and the modifying particles.
According to another variant embodiment, the evacuation device may be common for the activated particles and for the residual products.
A description is provided below of the method and device according to the invention, making reference to the appended drawings.